Volume control



Nov. 26, 1935. H. o. PETERSON VOLUME CONTROL Filed Jan. 13, 1930INVENTOR HAROLD o. PETERSON BY W M1 4, ATTORNEY Patented Nov. 26, 1935VOLUME CQNTROL Harold 0. Peterson, itiverhead, N. 1 assignor to RadioCorporation of America, a. corporation'of Delaware Application January13, 1930, Serial No..420,313:

2 Claims.

This invention relates to a volume controlled electrical system whereinit is desirable to maintain constant energy output from a variableenergy input.

5; In volume control schemes as applied to radio receivers, collectedsignal energy, varying in in tensity, is split into two portions andseparately rectified. One portion of the rectified energy is utilizedfor translation purposes and the other 101 for volume control so thatthe translation energy is maintained at a constant volume. Adisadvantage of the system described resides in the fact that separatedetectors are required, one for translation purposes and one forproviding recti- 153 fied signal energy for volume control. An object ofmy present invention is to reduce the number of tubes required forvolume control and I do this by utilizing one detector tube or electrondischarge device for supplying rectified energy 203.5 for bothtranslation and volume control. More specifically I accomplish thisobject by the use of a detector tube having an impedance associated withits output circuit. The detector rectifies the entire amount ofcollected or input en- 255 ergy; and, by virtue of the impedancereferred to, potential differences are set up thereacross which areutilized for controlling the bias on a preceding electronic amplifierthereby volume controlling the system. The remaining portion of theenergy appearing in the output circuit of the detector, rectifier ordemodulator, is utilized for translation purposes.

Moreover, in known volume control systems, grid biasing potentials areapplied to the recvtifier used for volume control, and the resultantanode current flow is utilized to vary the bias on the preceding radiofrequency amplifier. In such a system with the input energy very weak,there is little fiow of plate current which, as

already indicated is to be used for increasing the amplification of thepreceding amplifiers; and because of the small current flow, the systemtends towards instability. A further object of the present invention isto provide a volume controlling system wherein a large current flowcorresponds to a weak input and wherein the large current flow isutilized to control the amplification of the system. In this manner anytendency towards instability, for the reason mentioned, is effectivelyovercome.

Furthermore, in known systems, volume control is applied to only theradio frequency stages of a receiver. In order to improve sensitivity, afurther object of this invention is to apply volume control to theintermediate frequency amplifier of a heterodyne system; and, to stillfurther. ens hance volume controlling, it is a further object.

'of this invention to apply volume COIltIOl'lJObOth:

radio frequency and intermediate frequency amplifiers. 5.

If volume control biasing potentials are ap plied to the amplifiersinstantaneously; that? is.- to say, with every minute and quick. change.in; intensity of the input energy, the tendency: of

the volume control arrangement would be to de- 10.

stroy the modulation of the incoming; energy.. To avoid such an effectis a further object of my invention and this I accomplish by inserting.

istic of my invention are defined with particu- 20;

larity in the appended claims. However, it may best be understood bothas to its structural oreganization and method of operation by'referring;to the accompanying drawing in which Figure 1 shows my invention appliedto: ax

simple radio receiving circuit,

Figure 2 illustrates.my invention applied to-:a heterodyne receiver; and

Figure 3 is given to aid in the explanation; of:

the operation of my invention, 30,:

Fig. 4 shows the circuit connections for the. automatic volume control.arrangement used: in. Fig. 2.

Referring to Figure 1, radiated signal energy collected upon antenna 2'is fed through tunable circuit t to the input side of an amplifier.comprising electron discharge device ii of suitable. type,here shown asa vacuum tube having a screen grid and indirectly heat-ed: cathodes Al:.

though only one amplifier stage has'been shown,.

for the sake. of simplicity, any suitable number; may be utilized.Amplified energy, from amplia fier 6: having a tunable circuit 8; in theoutput: circuit thereof, is fed to rectifying or demodulating apparatusHl utilizing a single detector or rectifier it for rectifying ordemodulating all of the collected signal energy. The output of detectorI2 is fed to a suitable translating device such as phones It through, ifdesired, a suitable low frequency amplifier Iii of any well known 50type. In order to utilize the same detector for volume controllingamplifier 6 as Well as for supplying translation currents to translatingdevice l4, an impedance in the form of a resistance I8 is placed 55 inseries with the output electrodes of rectifier 12. By means of aconnection 20 between the output circuit of detector i2 and amplifier 5,the amplification thereof is varied inversely to the strength of theenergy collected on antenna 2 and dir ctly as the unidirectional outputcurrent flow of the detector l2. In this manner, a single rectifier l 2,is utilized to provide both translation and volume controllingpotentials.

In the ordinary type of detector utilized in the ordinary receivingcircuit, the grid or control electrode thereof is biased negatively by asuitable potential source. However, if such a scheme were utilized inconnection with detector l 2, with a weak incoming signal there would bea small current flow through resistance l8, resulting in unstablecontrol of amplifier 5. Therefore, to provide a large current flowthrough resistance i8 when the incoming collected energy is weak, I biasthe grid of tube !2 to a point such that in the presence of weak signalsthere is a large plate current fiow. Preferably I do this by the use ofa blocking condenser 22 and a grid leak 24 rather than by biasing thegrid 66 of the rectifier tube I2 positively. The relation of anodecurrent to signal strength for the tube i2 is shown diagrammatically inFigure 3 where, for small signal values, plate current is a maximum. Ihave found that the use of large current flow to in crease amplificationof the amplifier 6, materially improves stable action.

By virtue of the large unidirectional current flow through resistance I8too large voltages may be applied to the grid of the amplifier tube 6.To

"preclude this possibility I insert in connection 20 a source ofpotential 255 opposed to the voltages produced across resistance 58.Voltage control may further be assisted by the use of variable tap 28terminating connection 2%.

Biasing or control potentials applied to the radio frequency amplifier 5need not necessarily be limited to the input or control electrodesthereof but may, by the suitable choice of elements such as resistanceis and source of potential 26, be applied to the screen grid or anodethereof.

'Io smooth out the action of the volume con trolling apparatus and tomake it unresponsive to sudden changes in volume caused, for example, bysignal modulation of the collected high frequency energy, I associatewith the volume control connection 2% a time delaying circuit comprisingresistarice 3t and condenser 32. By suitable choice of values forresistance 38 and condenser 32, volume control action may be made asfast or as slow as desired.

My invention as applied to a heterodyne receiver is illustrateddiagrammatically in Figure 2. Electromagnetic energy collected upon asuitable antenna 49 is amplified by radio frequency amplifier 22 of anydesired number of stages. The amplified energy is fed into a modulator44 together with locally generated energy generated by means of agenerator 46. Beat frequency energy resulting from the modulation is fedinto and amplified by an intermediate frequency amplifier 48, the outputof which is detected or rectified by a suitable rectifier I ll similarto that shown in Figure l. The output of the detector l may then beamplified by amplifier 59 and translated by a suitable translatingdevice 52.

For volume control, connections 29' and 299 similar to connection 2!] ofFigure 1 are taken from detector Iii. As desired, volume control 10biasing potentials may be applied to the control electrodes, screengrids oranodes of the amplifiers, and they may be obtained from separateresistances placed in the output circuit of detector ill or preferablyfrom the same resistance using separate terminating taps for connectionsand zoo. Moreover, each connection 20, 200 may contain potential sourcesof the same or diiferent values as well as time delaying circuitssimilar to that shown in Figure 1. Fig. 4 shows 20 the latterconnections. The connection 200 between the intermediate frequencyamplifier and resistor 'l 8 includes the tap 28, voltage source 26',resistor 39' and condenser 32'. The detector l0 utilized in Figure 2 ispreferably given, as described, the characteristic shown in Figure 3whereby amplification of the amplifiers is varied in accordance with ordirectly as the unidirectional component appearing in the output circuitof the detector It; or, in other words, in- 80' versely to the strengthof the signal collected upon antenna 40.

Having thus described my invention what I claim is:

1. In combination with the radio frequency 35 and intermediate frequencyamplifiers of a superheterodyne receiver, a second detector of the leakygrid type, a biasing control path in the anode to cathode current pathof the detector, and independent direct current connections sole- 1yfrom said biasing path to an amplification control electrode of eachamplifier for regulating the gain of the amplifiers in a mannerinversely proportional tothe receiver signal input variation, saidconnections being made to points of different potential of said biasingpath.

2. In combination with the radio frequency and intermediate frequencyamplifiers of a superheterodyne receiver, a second detector of the leakygridtype, a biasing control path in the anode to cathode current path ofthe detector, and independent direct current connections solely fromsaid biasing path to an amplification control electrode of eachamplifier for regulating the gain of the amplifiers in a mannerinversely proportional to the receiver signal input variation, saidconnections being made to points of different potential of said biasingpath, and each connection containing a source of positive potential anda time delay network.

HAROLD O. PETERSON.

